The cost of prepainting would likely be highly dependent on the number of minis. If they're planning on having a bunch of minis tied to stretch goals, it could be hard to estimate that actual cost until the campaign actually ends.

After reading about what even happened with some of the Awakened Realms paint jobs, I think you're better off screening for an individual painting service. (Ironic, since Awakened Realms is a painting studio.)http://theminiaturespage.com/boards/topics.mv?id=34